My title for this book was "The Holiness of the Heart's Desire: A Sexual Ethics for My Children." (I was over-ruled by the marketing people, who always make the final decision on book titles.) It's written primarily for other parents who share my yearning for reasonable, non-dogmatic, persuasive terms in which to explain and defend the significance of sexual fidelity. The first step in that process, I'm convinced, is thinking through the issues coherently for ourselves, in fully adult terms that we can nonetheless translate in ways appropriate to the ages and situations of our kids. And so, I contend that sexual fidelity is best understood as a subset of interpersonal ethics-not as a variety of property rights. The applicable category is friendship: don't exploit; don't let yourself be exploited. From various angles I explain that we have an erotic need for fidelity, a psychological need for it, and a spiritual need for it as well. Faithful sexual relationships are ultimately holy; they reflect some of our deepest capacities for spiritual expression. (In passing, I observe that the same is true of faithful, committed same-sex relationships: orientation provides no moral excuse for promiscuity or sexual exploitation.)